Inspecting used cnc machines?

[cncwhiz]

Looking for some input from you guys as to what to check on a used cnc mill. We have made a list of things that we deem important to our manufacturing. This machine is a "HG400" with a seicos/sigma 10 controller and are aware of the fact that mori bought out hitachi seiki and getting parts is a PIA. All or our other machines have fanuc controls on the front side and micon slave controllers. Looks like the control is based off of a 16b fanuc control so I won't need a new post for the machine. They will all tell you that the machine only ran aluminum and only made light cuts. We bought two of our machines like this from back east and they had been machining cast iron. This machine we are going to look at tommrow. It is now in operation at applied technologies in Reno Nevada.

[Al_The_Man]

My experience is that Mori is not supporting Hitachi-Seiki parts and some of the electronics are hard to come by. I would pay a price for the mill accordingly.
I ended up custom manufacturing a power supply for a customer.
Al.

[cncwhiz]

Originally Posted by Al_The_Man My experience is that Mori is not supporting Hitachi-Seiki parts and some of the electronics are hard to come by. I would pay a price for the mill accordingly. I ended up custom manufacturing a power supply for a customer. Al.

AL,
We have some sources for hitachi seiki parts. There is also a guy named Josh innthe mid west that worked for hitschi and has more connections and software as well. If you need some of these contacts I can get them for you.

[One of Many]

I would put it through the paces in what matches my expectations for the value in the trade. At near surplus/scrap price there are a lot of things I could over look. The rarity of replacement parts can become a big issue while turning a hunk of iron into a white elephant!

If you can get into the parameter files, check for backlash and ball screw compensation settings, if there are any.

Take a good tenths indicator with you and run some tests on the backlash of all axis with the smallest resolution the machine will do. By moving positive or negative with the handwheel or jog feature, seeing the actual verses controlled move will show up on a reversal of direction. If it takes 6 steps to see any movement, decide what you can live with or if it is easily rectifiable. Check it in a few places along the screws. Large backlash compensations effect the whole screw, even where there is none.

A test program is another good trial. The first test would be to deck a 12" square block about 1 1/2-2" thick. Look for surface steps and true flatness for some idea of wear in the ways or spindle bearing slop/alignment.

I have also used a program called circle, diamond square(I've mentioned in other posts) that are all machined in the same 12" block. The circle is machined to a depth of 3/4", the diamond machined at 1/2" depth on top of the circle inscribed so the points should match the circle diameter. Then the square is machines on top of the diamond inscribed such that its corners run out at the diamonds 4 mid-point edges or circumscribed to a depth below the larger circle. This will reveal a lot about the machines ability to interpolate in all directions of x and y without any comps etc. The idea is to create these geometric shapes in steps to check dimensional accuracy and fluid motion for finish without gouges or goofy reactions to changes in direction, besides squareness in 2 orientations. These can be 1/8" steps, but at least enough to see any major issues of concern.

Another check would be to use a 2x4 to pry up under the spindle to indicate if there is any movement in the spindle bearings or head lead screw backlash. A quick indicator inspection of the spindle runout would be reasonable too. This may best be accomplished with a tool holder and a 6" long x 3/4-1" diameter drill blank just to see if the runout is excessive at x distance away from the holder.

Look at the boards in the machine or anything that appears to be a recent replacement or looks to have been disassembled and ask questions hoping they will give an honest answer.

DC

[Al_The_Man]

Originally Posted by cncwhiz AL, We have some sources for hitachi seiki parts. There is also a guy named Josh innthe mid west that worked for hitschi and has more connections and software as well. If you need some of these contacts I can get them for you.

Thanks, I will keep that in mind if I need any in the future.
Al.